Outlook cannot connect through a firewall or a proxy server that is performing Network Address Translation (NAT) between public and private networks in Outlook 2002 and Outlook 2003 (291615)
The information in this article applies to:
- Microsoft Office Outlook 2003
- Microsoft Outlook 2002
This article was previously published under Q291615
For a Microsoft Outlook 2000, Outlook 98 and Outlook 97 version of this article, see 238390.
For a Microsoft Outlook Web Access 5.5 version of this article, see 238954.
SYMPTOMS Microsoft Outlook clients cannot connect through a firewall or
proxy server that is performing Network Address Translation (NAT) between
public and private networks. CAUSE When the IP packets that contain the remote procedure call
(RPC) information are edited during translation, the IP packets lose the RPC
connectivity information. This causes the client not to connect to the server.
Additionally, Outlook can have problems resolving the name of the
Microsoft Exchange Server computer behind the firewall or proxy server.
WORKAROUND A work around for firewalls or proxy servers that are not
based on Microsoft Windows NT is to perform a one-to-one translation between
the two networks. This is also called "opening a pipe or tunnel" between the
public and private networks. This takes all requests for a specific address on
the public network and passes them directly to the private network. For
additional information on about how to configure a one-to-one translation,
please refer to your manufacturer's documentation
A one-to-one
translation or pipe does not work for Windows NT-based firewalls and proxy
servers because the Outlook client attempts to bind to the end-point
mapper port (EPM), port 135, on the firewall. This server does not return the
correct Exchange Server connectivity information to the Outlook client.
Another possible work around is to use Outlook Web Access. This only
requires allowing HTTP traffic through the firewall or proxy server.
| Modification Type: | Minor | Last Reviewed: | 10/1/2004 |
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| Keywords: | kbnetwork kbprb KB291615 |
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